The fabrication of semiconductor devices typically comprises a sequence of photolithography steps. During each photolithography step, the structure of a specific layer of the semiconductor device is transferred onto the (temporary) surface of the semiconductor device, for example, by exposing selected areas of a photo resist to ultraviolet light. The selective exposure of the photoresist can be done using a photo mask or by scanning the photo resist with an ultraviolet laser. The semiconductor device thus prepared then undergoes further processing steps, such as etching, ion implantation, or deposition of a material on the temporary surface of the semi-finished semiconductor device. In order to make useful devices the patterns for different lithography steps that belong to a single structure must be aligned to one another. To this end, a particular pattern may include a set of alignment marks. The alignment marks may be regarded as high precision features that are used as a reference when positioning subsequent patterns to the preceding pattern. This makes it possible to position a subsequent photo mask sufficiently precisely with respect to a preceding photo mask and to the structure that has been created in the meantime using the preceding photo mask.
Some semiconductor devices comprise one or more specially tuned layers of epitactically grown semiconductor material (EPI). The epitactically grown material is typically silicon, but may be another material, as well. Among others, power semiconductor devices or power integrated circuits (power ICs) which may be used as, e.g., a switch or rectifier in power electronics, are one example of using epitactically grown silicon. These power semiconductor devices or power ICs may be built using a vertical structure. One option for providing such a vertical structure of the semiconductor device is to use an epitaxy step during the fabrication of the semiconductor device.